Abstract

We demonstrate the presence of strong longitudinal electric fields (Ez) in silicon nanowire waveguides through numerical computation. These waveguide fields can be engineered through choice of waveguide geometry to exhibit amplitudes as high as 97% that of the dominant transverse field component. We show even larger longitudinal fields created in free space by a terminated waveguide can become the dominant electric field component, and demonstrate Ez has a large effect on waveguide nonlinearity. We discuss the possibility of controlling the strength and symmetry of Ez using a dual waveguide design, and show that the resulting longitudinal field is sharply peaked beyond the diffraction limit.

The (a) transverse (Ex) and (b) longitudinal (Ez) field components of the fundamental antisymmetric system mode supported by (c) dual waveguides where each waveguide has cross-section dimensions 260 × 500 nm2 separated by a 50 nm gap.

The(a)Ez and(b)Ex electric field components at the endface of dual 260 × 500 nm2 Si nanowire waveguides with SiO2 cladding, 50 nm gap, terminated into air, and excited by the fundamental antisymmetric system mode. (c) ∣Ez∣2 near the edge of the dual waveguide structure. Contour plot (d) and line scan (e) of ∣Ez∣2 40 nm from the edge of the waveguide.